Effects of Radiation on Conductivity and Dielectric Properties of Polymehtyl Methacrylate/Acrylic Acid Polymer Blends

The cation exchange membranes seem to be the most widely studied due to their appropriate properties for many applications including as solid polymer electrolytes for electrochemical devices in battery and fuel cell. Polymethylmethaacrylate /Acrylic acid (PMMA/AA) blends have been prepared by solvent casting method at different PMMA:AA ratios of 1:1, 1:2, 1:2.5, 1:3.0, 1:3.5 and 1:4.0 by weight. The samples were irradiated separately using 1.25-MeV γ-rays at different doses of 2, 4, 8 and 10 kGy and also with 1.25-MeV e-beam at doses of 50, 100, 150 and 200 kGy. The non-irradiated samples were also treated thermally at different temperatures of 300, 333, 342, 352 and 363 K. The dielectric properties and the electrical conductivity have been studied using an impedance analyzer at frequencies ranging from 20 Hz to 1 MHz. The dc conductivity, dc of un-irradiated and thermally untreated samples increases from 7.7x10-8 S/m to 3.27x10-7 S/m at 100 Hz when the composition ratio increases from 1:2.5 to 1:4 due to an increase of the number of free charge carriers, mainly ions introduced in the blends. The dielectric lost " at 100 Hz also increases from 9.32 to 621.03. However, at these concentration ratios, the dielectric constant, ' at 100 Hz decreases from 15.68 to 10.64 , attributed to decreasing effect of dielectric dipole as the amount of charge carriers introduced into the system increases. An increase of temperature from 300 K to 363 K increases the dc conductivity of 1:4 composition ratios from 1.1x10-5 S/m to 6.91x10-4 S/m at 100 Hz due to an increase of the ion mobility and thermal expansion occurred in the blends. By the temperature treatment the value of "at 100 Hz also increases from 10.35 to 10.04 x 103 with the temperature increases due to an increase of the mobility of free ions. An increase of ' value at 20 Hz from 10.35 to 15.38 with increasing temperature from 300 K to 363 K is due to increase the degree of dipole orientation as more dipoles in the samples align with the electric field. Upon irradiation with doses from 2 kGy up to 10 kGy, the polymer blends become grafted to Polymethylmethaacrylate-g-Polyacrylic acid (PMMA-g-PAA) blends, which increase the dc conductivity of 1:4 composition ratio from 2.13 x10-7 S/m to 6.07 x10-7 S/m at 100 Hz as the number of free and trapped ions increases. There is also an increase of " value at 100 Hz from 38.43 to 109.27 with the increase of dose from 2 kGy up to 10 kGy, due to the increase of ions within the irradiated materials. At the same time the dielectric constant value of ′ at 100 Hz increases from 9.98 to 22.83 as more dielectric dipoles are present due to the increase of grafting. As the dose increases from 50 kGy to 200 kGy after e-beam irradiation, the PMMA/AA polymer blends become PMMA/PAA copolymer composites. The dc conductivity of 1:4 composition ratio increases from 1.9x10-9 S/m to 1.29x10-8, when the dose increased from 50 kGy to 200 kGy, since more ions might be generated in the samples. The value of " at 100 Hz also increases from 0.34 to 2.32 , as more increase ions were introduced within the materials. The value of ′ at 100 Hz increases from 3.03 to 12.92, when the dose increased from 50 kGy to 200 kGy, attributed to the cross-linking between PMMA and PAA, which results in more dipoles formed in the co-polymer matrix.

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